The first thing most people think about when they start a diet is, "How many calories should I eat to lose weight?" You calculate how many calories your body needs, then by eating a smaller amount each day you should start to shed pounds. It does, however, involve daily calculations as well as an unhealthy - some might say - obsession with food nutrition labels to make sure your calorie intake is more or less accurate. At least, that's the idea.
Good old calories. They've been around for nearly 200 years and have been the mainstay of dieting since dieting began (at least, that's how it seems). But a growing number of nutrition experts are expressing doubts about them.
Last year, for instance, some researchers went public with the news that calorie counts on food labels could be inaccurate by up to 25."
So, for instance, if something says it contains 500 calories but requires 40 calories in terms of energy to be processed by your digestive system, then the real number of calories on the label should be 460.
If you're not convinced that makes enough of a difference to be significant, bear in mind that just by eating 20 more calories than you need each day for a year, you'll gain 2lb in weight.
Weight Watchers is the first of the big weight-loss companies to acknowledge what it calls the 'calorie delusion', and has made big changes to its own diet advice, launching a new plan called ProPoints as a result.
"Counting calories from food labels to lose weight is like judging a book by its cover - you're not getting the whole story," claims Weight Watchers dietician Zoe Hellman. "Through creating the ProPoints plan, we are making working with your body to lose weight a simple way of life."
Alternatives to calories such as ProPoints are nothing new, however, with the following all having surfaced during the past few decades:
Carbs Followers of the Atkins, Dukan and other high-protein, low-carb diets have learned to count carbs instead of calories, often with great results.
Fat Counting how many grams of fat you eat has also been popularised by people like Rosemary Conley, who claim a low-fat diet is the key to weight-loss success.
GI ratings Many dieters also swear by the GI system, which is based on the glycaemic index of foods (that is, how quickly any particular food releases sugar into the bloodstream) and which recommends avoiding all foods with a high GI.
Bites And there are many other systems of measuring and controlling how much you eat, even one called Diet Directives that suggests you should eat no more than 80 bites a day.
What do you think about calories? After 200 years, should we be moving on? Or is counting calories still the best way to lose weight?